The result of the parliamentary all-nighter that approved Greece’s latest multibillion-euro bailout on Friday morning means early elections are now a near certainty and could come as soon as next month.

The prime minister, Alexis Tsipras, may have secured parliament’s backing by a comfortable margin but he did so thanks to the support of the opposition, not of his own leftist Syriza party, nearly one-third of whose 149 MPs either voted against or abstained.

The rebellion by Syriza hardliners, furious at what they see as a betrayal of the party’s anti-austerity principles, left Tsipras short of the 120 votes – two-fifths of the 300-seat assembly – that Greek prime ministers need to show they command a majority and could survive a censure motion.

This time, he would not be able to count on the votes of the conservative New Democracy opposition, which has already said it would not back the government in a confidence vote – although some other pro-European parties might.

Win or lose, however, Tsipras is now widely expected to try to shore up his position by going to the polls this autumn. Fresh elections could be held at a month’s notice, making late September or early October likely dates.

“The agreement has cost the government its majority,” Nikos Xydakis, the culture minister, told state television. “As things have turned out, the clearest solution would be elections.”

Tsipras told parliament he did not regret his “decision to compromise” with Greece’s international creditors: “We undertook the responsibility to stay alive, over choosing suicide.”

The depth of the rebels’ bitterness is plain. Zoe Konstantopoulou, the speaker, raised so many procedural questions and objections that the finance minister, Euclid Tsakalotos, missed the 9.30am vote, Reuters reported, as he had to catch a plane to Brussels.

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“Every corner and beauty of Greece is being sold,” Konstantopoulou declared. “The government is giving the keys to the troika [of creditors], along with sovereignty and national assets … I am not going to support the prime minister any more.”

But it is unclear how much popular backing the rebels would get. Analysts argue that while it would create political uncertainty, Tsipras has every interest in calling a snap election, before the punishing terms of the new bailout make themselves felt. The youthful prime minister still enjoys great personal popularity in Greece for having at least tried to stand up to German and eurozone austerity demands.

With rebellious hardliners sidelined in a new anti-euro movement that polls suggest only a minority of Greeks would support, the prime minister could hope to capitalise on the continued disarray of the conservative opposition. Recent polls predict he would win.